Agricultural vehicles, such as tractors, typically include a pair of braked rear wheels with a right hand brake pedal and a left hand brake pedal. In such systems, the right hand brake pedal can be applied alone causing just the right hand rear brake to be applied, and similarly the left hand brake pedal can be applied alone causing just the left hand brake to be applied. Applying say just the right hand brake, whilst simultaneously steering the front wheels fully to the right, enables the tractor to turn more sharply than by using steering alone. This can be particularly useful when turning a tractor with a tractor mounted implement, such as a plough at a headland (i.e., the unploughed land at ends of furrows or near a fence) of a field. To engage both of the rear brakes simultaneously, such as for normal service braking, the right and left hand brake pedals are simultaneously applied.
A problem of agricultural brake systems of the above type is that when both brake pedals are simultaneously applied, a system must be present to balance the pressure being applied to the right and left hand brakes. Absent such a system, increased brake pressure in one side compared to the other would result in unexpected turning of the vehicle when both brakes are applied. One such known brake system is disclosed in U.S. Pat. No. 4,408,805.